1. Field of the Invention
The present invention relates to a deinking agent which is used for the reclamation of waste paper such as newspapers and magazines. More particularly, the present invention relates to a deinking agent which yields deinked pulp having a higher b value and containing a lower amount of sticky substance when used for the deinking treatment by floatation method, washing method, or a compromise method thereof.
2. Description of Related Art
The reclamation of waste paper such as newspapers and magazines is an old practice. An importance is being attached to the effective reclamation of waste paper because of the recent supply shortage and price hike of pulp sources. In addition, deinked pulp is finding more valuable uses than before. On the other hand, the reclamation of waste paper is becoming more difficult from the standpoint of deinking because of recent changes in printing technology, printing methods, and printing ink, as well as the utilization of waste paper which was never been reclaimed in the past. For more effective deinking, improvements are being made on the existing machine.
A variety of chemicals have been used to separate and remove ink and other impurities from waste paper. They include alkali agents (such as sodium hydroxide, sodium silicate, sodium carbonate, and sodium phosphate), bleaching agents (such as hydrogen peroxide, hyposulfite, hypochlorite), and sequestering agents (such as EDTA and DTPA), and deinking agent. Examples of the deinking agent include anionic surface active agents (such as alkylbenzenesulfonate, higher alcohol sulfate ester salt, .alpha.-olefinsulfonate, and dialkylsulfosuccinate) and nonionic surface active agents (such as an adduct of a higher alcohol, an alkylphenol or a fatty acid and an alkanolamide). These agents may be used singularly or in combination with one another.
Unfortunately, the conventional deinking agent is poor in ink catching performance although it is good in foaming performance when used in the floatation process. Also, when it is used in the washing process, it is poor in detergency and generates a large amount of foam which causes trouble during draining. Thus, with the conventional deinking agent it was only possible to obtain deinked pulp of low grade.
Moreover, deinked pulp obtained by using the conventional deinking agent is limited in its application area because it looks dark and dull. Thus, it can only be used in a reduced amount in paper board and newsprint paper. To eliminate the dull appearance, it is necessary to use more bleaching agent than is required for deinking. One way of producing deinked pulp having a bright color tone is to increase the b value. It is possible to increase the b value if an alkaline agent is used in large quantities. However, this increases the amount of sticky substances and the water discharge load an makes the resulting pulp brittle. There has been no effective means to eliminate these disadvantages.
The present inventors proposed using as a deinking agent a reaction product obtained by adding an alkylene oxide to a mixture composed of a natural fat or oil and a tri- or polyhydric alcohol (See Japanese Patent Laid-open No. 239585/1985.)
After careful examination of its behavior in the deinking process, it was found that an agent composed of a natural fat or oil and a tri-or polyhydric alcohol in a molar ration of 1:0.5 to 1:3 causes foaming troubles in the floatation step, dehydration step, draining step, and papermaking step. Moreover, it does not completely eliminate the dull appearance although it does provide deinked pulp having a high degree of whiteness.